Prosthetic devices may be used to repair a variety of body parts. For example, expandable devices such as fusion cages may provide a stabilized opening for inserting a bone graft between adjacent portions of bone. In time, the bone and bone graft can grow together through or around the fusion cage to fuse the graft and the bone solidly together. Current uses of fusion cages include treating a variety of spinal disorders, including degenerative disc diseases, Grade I or II spondylolistheses, adult scoliosis and other disorders of the lumbar spine. Spinal fusion cages are often inserted into the intervertebral disc space between two vertebrae for fusing them together. Such fusion cages can distract or expand a collapsed disc space between two vertebrae to stabilize the vertebrae by preventing the vertebrae from moving relative to each other.
A typical fusion cage is generally cylindrical, hollow, and threaded. Alternatively, some fusion cages are unthreaded or made in tapered, elliptical, or rectangular shapes. Known fusion cages are generally constructed from a variety of materials including titanium alloys, porous tantalum, other metals, allograft bone, carbon fiber or ceramic material.
Fusion cages may be used to connect any adjacent portions of bone or other solid body parts. However, one standard use of fusion cages is in the spine. Although often used in the lumbar spine, fusion cages can also be used in the cervical or thoracic spine. Fusion cages can be inserted in the spine using an anterior, posterior, or lateral approach. Insertion is usually accomplished through a traditional open surgery which can be traumatic to the patient and require weeks, if not months, of recovery.
General techniques for inserting fusion cages are known. For example, insertion techniques and details on the design of fusions is described in Internal Fixation and Fusion of the Lumbar Spine Using Threaded Interbody Cages, by Curtis A. Dickman, M. D., published in BNI Quarterly, Volume 13, No. 3, 1997, which is hereby incorporated by reference. For example, many threaded fusion cages are inserted by first opening the disc space between two vertebrae of the lumbar spine using a wedge or other device on a first side of the vertebrae. Next, a tapered plug may be inserted into the spine at the site of the disc that is being replaced with the expandable device. The plug may be used to hold the disc space open in the case of a threaded, cylindrical cage insert. A threaded opening may then be then drilled and tapped on a second side of the spine that is opposite the side used for accessing the first plug. This double access thereby produces the equivalent of a “split” threaded bore defined by the walls of the vertebrae above and below the bore. The threaded expandable device may then be threaded into the bore and the wedge removed. The first side may then be drilled and tapped before inserting a second threaded expandable device. Typically, two threaded expandable devices are used at each intervertebral disc level.
Traditionally, back surgery to insert a fusion cage has been done using an incision that was larger than the part being delivered to the spine. In this way, surgeons were able to deliver medical devices to the desired site without undue concern regarding the size of the medical device. However, with the development of small incision techniques such as arthroscopic surgery and/or kyphoplasty, it is generally preferred to be able to deliver medical devices through smaller incisions. The ability to perform the surgery with a smaller incision ultimately results in faster healing times for patients. In some instances, it is desired to be able to deliver one or more medical device(s) through a cannula. However, as the cannula generally has a small diameter, such devices may need to be expanded to a larger state to perform the role required.
Thus, it would be beneficial to provide an expandable device that can be delivered percutaneously (e.g., via a cannula) to the body part of interest and then expanded in situ. The expandable device could also be designed to allow the expandable device to be expanded in the body part of interest while minimizing trauma to the adjacent tissue. Such expandable devices would be useful for repair of the spine or other body parts.